Ethanol extract of allium cepa has been evaluated as a green corrosion inhibitor for ?-brass in HNO3 solutions using weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. Potentiodynamic polarization measurements showed that this extract acts as a mixed type inhibitor. The inhibition efficiency increases with increasing the extract concentration, but decreases with raising the temperature. The adsorption of allium cepa on the ?-brass surface follows Temkin adsorption isotherm. From EFM the causality factors are very close to theoretical values which indicate that the measured data are of good quality. Nyquist plots show a single capacitive loop in uninhibited and inhibited solutions. Allium cepa has antifaugal and antibacterial effect.